European Patent Application 1 879 426 discloses a binaural hearing system in which sound information and control information present in or received by one of the hearing aids is relayed to the respective other hearing aid in order to make the information available in both hearing aids. Relaying may be unidirectional or bidirectional. The document does not disclose any details as to how the relaying is implemented. US Patent Application 2007/0269049 discloses a similar system.
U.S. Pat. No. 7,529,565 discloses a hearing aid system, wherein a sender waits to send a message until expiration of a random time period after the wireless channel becomes free. The sender retransmits its message if it does not receive an acknowledgement from the intended receiver due to a collision with a transmission from another sender.
US Patent Application 2007/0009124 discloses a hearing aid system comprising a left-ear hearing aid, a right-ear hearing aid and a number of auxiliary devices. The hearing aids and the auxiliary devices together form a wireless network, via which they communicate with each other. Start-up of the network and admission of new devices to the network are controlled by a network master, which engages in an initialisation procedure with the new device(s). The network master is preferably one of the hearing aids, because this device is assumed to be always present on the network.
The head of a hearing-device user substantially disturbs the radio signals transmitted and received by the hearing devices, when these are in place at or in the user's ears. Consequently, the quality of the wireless communication between the hearing devices and the other devices on the network varies when the user moves his head. Such variations may lead to temporal gaps in the communication, and the duration of the gaps may vary from a few fractions of a second to several seconds or even minutes. The gaps may cause pauses and/or delays in audio signals presented to the user, e.g. during streaming of a television audio signal to the hearing devices. For a user of a binaural hearing system, such pauses and delays may be perceived as if sound sources disappear or shift their locations abruptly, which may be very annoying. Such effects may be even more pronounced, when the pauses or delays affect the left-ear and the right-ear hearing device differently. Furthermore, in a hearing system which communicates settings of one of the hearing devices to the other hearing device via radio signals, temporal gaps may cause the hearing devices to become temporarily unsynchronised, which may produce similar or other annoying audible effects.
In connection-based networks, as e.g. described in US 2007/0009124 mentioned above, gaps of longer duration may further lead to devices becoming disconnected from the network. To recover from such a long gap and allow the disconnected devices to participate on the network again, an initialisation procedure must be executed. The execution of the initialisation procedure may prolong pauses and/or delays in the audio signals presented to the user, thus worsening the problem. The execution of the initialisation procedure may take longer time if several devices become disconnected at the same time, e.g. if the network master is unreachable during a long gap.